Let's go back in time a little.
Not longer after Alice's mother chased her out of the house an opportunity presented itself in the form of a police raid. The zoo had always had to deal with a nosy cop here and there, but having connections with the powerful protected their operation for a long time. Unfortunately for them that protection breed arrogance. For a while now, they main way to deal with problems was to turn people into animals. But a few days before Princess was Princess they acquired a parrot that was once a son of a very powerful man.
Swat got all the human in the same room, including the caretaker and they didn't care to close Princess door properly and she was not going to let the opportunity pass. The mare immediately tried to find a the exit, but having to avoid the officers, she was eventually led to the labs. That's when another opportunity presented itself.
Being stuck in the labs for now, she took her time to read the vial that were around the place. Eventually she saw the words that gave her hope, "experimental cure". Being a mare had been hell, the idea she might be in a worse place by drinking the liquid didn't even cross her mind, and she gobbled it. At first she didn't feel anything, but soon a heat on her behind. In a second Princess was rocked by an orgasm, then another, and another and with each she started to morph. Her fur stared to fall and give way to smooth skin, her mane became her hair and the tail was absorbed back into her back. But not everything was going her way. Two breasts started to grow on her chest and her vagina didn't go away, in fact it looked like a hybrid between a human and horse one, with dark labia but human form. Princess was no longer a mare, but a blonde woman.
Despite not having everything she wanted, the woman was more than happy to be human, and a human can sneak around much easier, even with vial on her hands.
Back in her parents house, after sneaking out of the zoo, Princess went to work on the ponies. It was hard to make both drink it but she somehow managed it. Her mother soon started to spurt her seed over the yard and change, much like her father. Much like Princess, her mother kept an equine penis and balls, although in a more human proportion and her father a hybrid mare-human vagina. The difference was that the rest of their bodies was like they were before, her mother was still a woman and her father a man, but both were extremely confused. They had lost their humanity not long ago, and now they were struggling with it's return, and with the face they didn't recognize. "Mom dad it's me!". His mother instinctively smelled the woman and managed to recognize the scent of her son under the still present scent of a mare.
Princess looked back and saw a goat looking straight at them from a window across the street. That was Kate White's house, and a good friend of Alice lived there, so that might be where she was. She rushed to the house, almost kicking the door open as she apologized to Kate in the couch. Upstairs a male goat was interacting with Alex, Melanie's brother and the female one rushed to you. "Alice, is that you? Its me, Prince. I'll fix this, drink this". She did quickly drink all the contents of the vial, as she had seen her parents revert back. Even if this wasn't her brother, he had some of her trust after that. Melanie got the last vial, and both returned to normal, completely this time. Princess cursed at the unreliability of the cure, as she was most likely stuck as a woman forever.
Alex had little time to get his bearings, but soon Kate and Alice's parent's climbed the stairs. Is this an end? Or merely a beginning?